The present invention relates generally to a method for treating the surface of plastic substrates and, more particularly, to a plastic media blast system adapted to improve the adhesion characteristics of the plastic substrate surface upon substrate application of a coating thereon.
With respect to the recent growth in automotive, aerospace, and aeronautical applications using advanced plastics and composite substrates, a related area of concern involves the ability to apply one or more layers of a protective and/or cosmetic coating thereon. More particularly, for various plastics materials, it is often difficult to achieve acceptable adhesion of the coating because of the non-profiled, smooth or otherwise slick surface properties typically associated with such materials. As such, poor coating adhesion results in an excessively high rate of product "rejects" being produced following the coating process, as well as increased incidences of product warranty claims, both of which result in significant rework or scrap costs to the manufacturing concern.
Conventionally, various chemical techniques are used for improving the adhesion characteristics of plastic substrates, such as the application of etchants, saline solutions or the application of an intermediate surface activation coating. In addition, adhesion promoters, as components of the coating material, are sometimes used as is flame heat treatment of the plastic substrate surface to be coated. However, with the advent of more stringent regulatory policies governing the transport and disposal of toxic chemical solutions, waste and the like, a greater emphasis is now being placed on development and utilization of non-chemical surface treatment methods.
Several non-chemical surface preparation methods, such as sand or grit blasting, are used for cleaning the surface of metal substrates before painting. Unfortunately, these techniques are not suitable for substrates made from plastic or a reinforced composite material since such abrasive blasting causes excessive damage to the surface. For example, with glass-fiber reinforced plastics, a surface preparation technique should not penetrate through the plastic to the underlying fibers. In the case of objects moulded of a plastic material, the outermost surface layers are typically harder and less porous than the underlying material. Under both scenarios, any excessive damage caused to the outermost layers during pre-coat surface treatment, may allow the coating to soak into the underlying material and give a non-uniform appearance.